Basic Cycle for TXV Systems

A second style of metering device that is used in many AC systems is the thermal expansion valve (TXV). The TXV metering device has been used for many years and is increasing in use in recent years because it varies the flow rate based on operating conditions. There are two styles of TXVs in use: the standard type and the block type. The standard type TXV is almost always located inside the duct box, while the block style is almost always located on the firewall.

As stated, the TXV metering device varies the flow rate through the valve based on operating conditions. This variable operation occurs by the valve sensing the temperature of the exit line of the evaporator and changing the internal opening as the temperature changes. When the sensing element is exposed to warm temperatures, the valve opens, and when the sensing element is exposed to cold temperatures, the valve closes. The continual opening and closing helps control the temperature in the evaporator core, which helps prevent the temperature from reaching freezing levels, which would cause the core to form ice on the surface.

Thermal expansion valves (TXVs) are a popular choice to use as a metering device to feed low-pressure atomized liquid into the evaporator core. The two types of TXVs include the block type (left) and standard type (right). Both styles operate by varying the opening inside the valve to feed refrigerant into the evaporator

Block type TXVs are located near the firewall and are visible from under the hood. O-rings and metal gaskets are used to seal the lines to the body of the

Standard-type TXVs are usually located inside the duct box and sealed with O-rings. It is important to make sure that the sensing element is securely attached to the exit line of the evaporator core so that it can accurately sense the temperature of this line. The valve opens up when the sensing element is warm and the valve closes when the sensing element is

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